The present invention relates to a fermentation process for preparing erythritol in high productivity with a novel mutant of Torula sp. DS101, more specifically, for preparing erythritol using mother liquor produced from purification process of palatinose, which comprises 30.about.60% of trehalulose, 10.about.30% of palatinose, 5.about.15% of fructose, 5.about.25% of glucose and 0.about.10% of sucrose.
Erythritol is a four-carbon polyol with property similar to other polyols currently used as food ingredients, such as, xylitol, sorbitol, manintol, maltitol, lactitol and isomalt. It is a naturally occurring substance and is widely distributed in nature. Erythritol is a metabolite or storage compound for seaweed and mushrooms. Fruits like melons, grapes and pears contain erythritol. It occurs frequently in fermented foods including wines and beers, and processed vegetables, such as, soy sauce and oriental miso bean paste.
Erythritol has sweetness with 60.about.70% of sucrose in a 10% solution. Its high negative heat of solution provides the crystalline material with a strong cooling effect. Erythritol can be safely used in foods to make them tooth-friendly. This property causes the inability of dental caries by developing bacteria to use erythritol as a fermentation substrate. Erythritol as a small molecule has strong colligative properties, such as, strong freezing point depression, boiling point elevation and high osmotic pressure. With its low hygroscopicity and viscosity in solution, it is very useful to reduce and control the water activity of foodstuff.
Erythritol can be produced by microbial methods using the osmophilic yeasts, especially species of the genus Torulopsis such as T. magnoliae, T. veratilis, and T. candida; Endonycopsis chodati; Hansenula supelliculsa; Pichia miso; Monilliella tomentosa var. pollinis; Trigonopsis variabilis; Trichosporonoides; Candida zeylanoides; and Aureobasidium sp. Monilliella tomentosa var. pollinis on the medium containing 33.about.37% of glucose with 43.about.48% of erythritol yield. However, erythritol production using such strains could not be applied to industrial scale due to the formation of by-products, such as, glycerol and ribitol.
On the other hand, industrial production of erythritol has been performed using a mutant of Aureobasidium. The mutant was isolated and developed by cooperative study of Nikken Chemical and National Food Research Institute of Japan. The mutant produced erythritol with 1.8.about.1.9 g/L.multidot.h volumetric productivity and 42.about.44% yield in the medium containing 40% of glucose. This has been regarded as the highest report of erythritol productivity and yield among the erythritol-producing microorganisms.
It has not been previously reported that Torula sp. produces erythritol. However, the inventors found that a mutant of Torula sp. isolated from a 40% of sucrose solution produces erythritol.